In 1907, Andrews began to oversee the plans for a new superliner, the RMS Olympic for the White Star Line. The Olympic and its sister ship the Titanic, which began construction in 1909, were designed by William Pirrie and general manager Alexander Carlisle along with Andrews. As he had done for the other ships he had overseen, Andrews familiarised himself with every detail of the Olympic and Titanic, in order to ensure that they were in optimal working order. Unfortunately, Andrews's suggestions that the ship have 46 lifeboats (instead of the 20 it ended up with) as well as a double hull and water tight bulkheads that went up to B deck, were overruled.
Andrews headed a group of Harland and Wolff workers who went on the maiden voyages of the ships built by the company (the guarantee group), to observe ship operations and spot any necessary improvements. The Titanic was no exception, so Andrews and the rest of his Harland and Wolff group travelled from Belfast to Southampton on Titanic for the beginning of her maiden voyage on 10 April 1912. During the voyage, Andrews took notes on various improvements he felt were needed, primarily cosmetic changes to various facilities. However, on 14 April, Andrews remarked to a friend that Titanic was "as nearly perfect as human brains can make her."
On 14 April at 11:40 PM, the Titanic struck an iceberg on the ship's starboard side. Andrews had been in his stateroom, planning changes he wanted to make to the ship, and barely noticed the collision. Captain Edward J. Smith had Andrews summoned to help examine the damage. Andrews and Captain Smith discussed the damage to the ship shortly after midnight, after Andrews had toured the damaged section of the ship and received several reports of the vessel's damage. Andrews determined that the first five of the ship's watertight compartments were rapidly flooding. Andrews knew that if more than four of the ship's compartments flooded, it would inevitably sink. He relayed this information to Captain Smith, stating that it was a 'mathematical certainty', and adding that in his opinion, the vessel had only about an hour before it completely sank. He also informed Smith of the severe shortage of lifeboats on board the ship.
As the evacuation of the Titanic began, Andrews tirelessly searched staterooms telling the passengers to put on lifebelts and go up on deck.[3] Several survivors testify to have met or spotted Andrews several times. Fully aware of the short time the ship had left and of the lack of lifeboat space for all passengers and crew, he continued to urge reluctant people into the lifeboats in the hope of filling them as fully as possible.